The invention relates to an aerosol can with a pressure reduction valve between the interior of the can and a spray valve, wherein, viewed in the outflow direction downstream of a closing site, a pressure chamber is provided for pressure regulation, in which a piston can be moved which closes the closing point against the force of a spring, for example a helical spring or a gas pressure spring, when pressure in the pressure chamber rises above the standard pressure.
For regulating the pressure in connection with aerosol cans filled with compressed gases, it is required to install a pressure regulating valve upstream of the spray valves which, with a filling pressure of approximately 10 bar inside the can, provides a standard pressure of approximately 2 to 4 bar. Pressure reduction valves with spring-loaded pistons are already known for this purpose, which provide the closing of a pressure-regulated closing site when the regulated pressure rises. However, with the known solutions the exiting aerosol flows around the cylinder/piston unit, so that an elaborate dual-walled housing structure is required. Such a solution has been described, for example, in WO 01/09009 A1.
The object of the present invention is to create a spray can with a pressure reduction valve which is easier to produce in comparison with already known embodiments.
In accordance with the invention, this object is attained by means of a spray can of the type described at the outset, wherein the connection between the closing site for pressure regulation and the spray valve is provided by means of a center bore in the piston.
The aerosol spray can in accordance with the invention offers the advantage that it is not necessary to provide an additional housing wall for conducting the aerosol around the cylinder/piston unit, so that the production outlay is reduced. The slightly increased thickness, for example of a piston rod used for regulating the closing site, poses no problems here.
In a preferred embodiment of the aerosol spray can in accordance with the invention there is no flow-through of the pressure chamber, so that an effect by dynamic occurrences on the accuracy of regulation in the area of the piston must only be feared to a lesser degree.
In a particularly preferred embodiment of the invention it is provided that the piston of the pressure reduction valve is accessible from the outside in such a way that it can be mechanically moved into its position in which it clears the closing site.
Such an embodiment, which can only be achieved with a large outlay in connection with a pressure reduction valve around which an outer flow occurs, permits a problem-free filling process, in which the piston is prevented from moving into its closed position, or at least into a position in which its opening cross section is reduced and the filling process therefore made more difficult under the very high pressure charge from the outside then occurring. An end stop preferably limits the opening stroke in order to prevent in this case damage to undefined contact points between the piston and the housing.
Alternatively to a mechanical displacement of the piston in its position in which it releases the closing site, the provision of some sort of overpressure valve is also conceivable which, in case of a pressure charge from the outside which considerably exceeds the interior can pressure, clears an opening to the can interior. However, this means an increased structural outlay.
In a preferred embodiment of the invention,it is provided that the closing site is formed between a sealing element fixed on the housing and a piston rod, or a separate element, which can be axially moved through the piston.
In the simplest case the piston and the piston rod can be embodied in one piece, wherein the sealing element preferably rests against the exterior circumference of the piston rod and closes a radial opening to its central bore in the closing site. With such a solution it is also conceivable that the sealing element clears the closing site in case of a pressure charge from outside which considerably exceeds the interior can pressure.
It is also alternatively conceivable to provide a separate closing element for forming the closing site with the sealing element, which can be moved into a position where it is lifted off the sealing element by means of a piston rod in case of a pressure drop.
The connection between the pressure chamber and the areas through which the flow passes can be provided either by means of an annular groove around the piston rod, which is connected with the closing site, or also by means of a radial bore in the piston rod, which provides the required active connection without the exiting aerosol flowing through the pressure chamber.
Embodiments of piston rods without radial bores are open at their front ends and are embodied to be laterally slit in this area in order to assure the flow-through of the aerosol.
A particular advantage of the aerosol spray can of the invention lies in that it is possible to provide a housing for the pressure reduction valve which supports the sealing element of the closing site and whose exterior wall delimits the pressure chamber on the inside. The spring of the pressure reduction valve, which is embodied as a helical spring or a gas pressure spring, is arranged between the housing and the piston, wherein the spring is preferably supported on a housing insert, which is locked, pressed, welded and/or glued together with the cylinder wall of the housing. The space between the housing and the piston in which the spring is arranged is preferably pressure-sealed toward the can interior in order to avoid an effect on the pressure regulation by penetrating aerosol. The space-saving construction of the pressure valve of a spray can in accordance with the invention permits the provision of the largest possible piston diameter, along with a corresponding adaptation of the force of the piston spring, and in this way the optimization of the regulation accuracy. A pressure gas cushion, which constitutes a gas pressure spring, can also be enclosed in the sealed space between the housing and the piston.